Two dielectric relaxation loss peaks associated with oxygen-ion diffusion in the intergrowth Bi2WO6-Bi3TiNbO9(Bi5TiNbWO15) bismuth layered ferroelectrics were observed. The activation energy and the relaxation time at infinite temperature, for these two peaks, were determined to be (0.89 eV, 1.3 x 10(-13) s) and (0.84 eV, 3.6 x 10(-10) s). The ac impedance spectroscopy indicated that the Bi5TiNbWO15 ceramic is an ionic conductor with an electrical conductivity of approximately 2.6 x 10(-2) S/cm at a temperature of 1073 K. (c) 2005 American Institute of Physics.